Cabazitaxel versus abiraterone or enzalutamide in poor prognosis metastatic castration-resistant prostate cancer: a multicentre, randomised, open-label, phase II trial

BACKGROUND

Treatment of poor prognosis metastatic castration-resistant prostate cancer (mCRPC) includes taxane chemotherapy and androgen receptor pathway inhibitors (ARPI). We sought to determine optimal treatment in this setting.

PATIENTS AND METHODS

This multicentre, randomised, open-label, phase II trial recruited patients with ARPI-naive mCRPC and poor prognosis features (presence of liver metastases, progression to mCRPC after <12 months of androgen deprivation therapy, or ≥4 of 6 clinical criteria). Patients were randomly assigned 1 : 1 to receive cabazitaxel plus prednisone (group A) or physician's choice of enzalutamide or abiraterone plus prednisone (group B) at standard doses. Patients could cross over at progression. The primary endpoint was clinical benefit rate for first-line treatment (defined as prostate-specific antigen response ≥50%, radiographic response, or stable disease ≥12 weeks).

RESULTS

Ninety-five patients were accrued (median follow-up 21.9 months). First-line clinical benefit rate was greater in group A versus group B (80% versus 62%, P = 0.039). Overall survival was not different between groups A and B (median 37.0 versus 15.5 months, hazard ratio (HR) = 0.58, P = 0.073) nor was time to progression (median 5.3 versus 2.8 months, HR = 0.87, P = 0.52). The most common first-line treatment-related grade ≥3 adverse events were neutropenia (cabazitaxel 32% versus ARPI 0%), diarrhoea (9% versus 0%), infection (9% versus 0%), and fatigue (7% versus 5%). Baseline circulating tumour DNA (ctDNA) fraction above the cohort median and on-treatment ctDNA increase were associated with shorter time to progression (HR = 2.38, P < 0.001; HR = 4.03, P < 0.001). Patients with >30% ctDNA fraction at baseline had markedly shorter overall survival than those with undetectable ctDNA (HR = 38.22, P < 0.001).

CONCLUSIONS

Cabazitaxel was associated with a higher clinical benefit rate in patients with ARPI-naive poor prognosis mCRPC. ctDNA abundance was prognostic independent of clinical features, and holds promise as a stratification biomarker.

Renal medullary carcinoma and its association with sickle cell trait: a case report and literature review

Renal medullary carcinoma (rmc) is a rare and aggressive renal malignancy that usually presents at an advanced stage, has a poor prognosis, and is associated with sickle cell trait. We present a case of rmc including radiologic and pathology findings, treatment, and outcome. A review of the literature is also presented, with an emphasis on the association of rmc with sickle cell trait, which was an unknown diagnosis in our patient preoperatively.

Real-world outcomes of nivolumab and cabozantinib in metastatic renal cell carcinoma: results from the International Metastatic Renal Cell Carcinoma Database Consortium

Objectives

In the present study, we explored the real-world efficacy of the immuno-oncology checkpoint inhibitor nivolumab and the tyrosine kinase inhibitor cabozantinib in the second-line setting.

Methods

Using the International Metastatic Renal Cell Carcinoma Database Consortium (imdc) dataset, a retrospective analysis of patients with metastatic renal cell carcinoma (mrcc) treated with nivolumab or cabozantinib in the second line after prior therapy targeted to the vascular endothelial growth factor receptor (vegfr) was performed. Baseline characteristics and imdc risk factors were collected. Overall survival (os) and time to treatment failure (ttf) were calculated using Kaplan-Meier curves. Overall response rates (orrs) were determined for each therapy. Multivariable Cox regression analysis was performed to determine survival differences between cabozantinib and nivolumab treatment.

Results

The analysis included 225 patients treated with nivolumab and 53 treated with cabozantinib. No significant difference in median os was observed: 22.10 months [95% confidence interval (ci): 17.18 months to not reached] with nivolumab and 23.70 months (95% ci: 15.52 months to not reached) with cabozantinib (p = 0.61). The ttf was also similar at 6.90 months (95% ci: 4.60 months to 9.20 months) with nivolumab and 7.39 months (95% ci: 5.52 months to 12.85 months) with cabozantinib (p = 0.20). The adjusted hazard ratio (hr) for nivolumab compared with cabozantinib was 1.30 (95% ci: 0.73 to 2.3), p = 0.38. When adjusted by imdc criteria and age, the hr was 1.32 (95% ci: 0.74 to 2.38), p = 0.35.

Conclusions

Real-world imdc data indicate comparable os and ttf for nivolumab and cabozantinib. Both agents are reasonable therapeutic options for patients progressing after initial first-line vegfr-targeted therapy.

Outcomes of patients with metastatic renal cell carcinoma that do not meet eligibility criteria for clinical trials

BACKGROUND

Targeted therapies in metastatic renal cell carcinoma (mRCC) have been approved based on registration clinical trials that have strict eligibility criteria. The clinical outcomes of patients treated with targeted agents but are ineligible for trials are unknown.

PATIENTS AND METHODS

mRCC patients treated with vascular endothelial growth factor-targeted therapy were retrospectively deemed ineligible for clinical trials (according to commonly used inclusion/exclusion criteria) if they had a Karnofsky performance status (KPS) <70%, nonclear-cell histology, brain metastases, hemoglobin ≤9 g/dl, creatinine >2× the upper limit of normal, corrected calcium ≥12 mg/dl, platelet count of <100 × 10(3)/uL, or neutrophil count <1500/mm(3).

RESULTS

Overall, 768 of 2210 (35%) patients in the International Metastatic RCC Database Consortium (IMDC) were deemed ineligible for clinical trials by the above criteria. Between ineligible versus eligible patients, the response rate, median progression-free survival (PFS) and median overall survival of first-line targeted therapy were 22% versus 29% (P = 0.0005), 5.2 versus 8.6 months, and 12.5 versus 28.4 months (both P < 0.0001), respectively. Second-line PFS (if applicable) was 2.8 months in the trial ineligible versus 4.3 months in the trial eligible patients (P = 0.0039). When adjusted by the IMDC prognostic categories, the HR for death between trial ineligible and trial eligible patients was 1.55 (95% confidence interval 1.378-1.751, P < 0.0001).

CONCLUSIONS

The number of patients that are ineligible for clinical trials is substantial and their outcomes are inferior. Specific trials addressing the unmet needs of protocol ineligible patients are warranted.

Sunitinib-related macrocytosis in patients with advanced renal cell cancer (RCC)

15580

Background: Sunitinib is an oral multi-targeted tyrosine kinase inhibitor with anti-tumor and anti-angiogenic activity approved and widely used for the treatment of advanced RCC. Based on a clinical observation that several RCC patients receiving Sunitinib developed macrocytosis, this study was performed to describe and examine macrocytosis in this patient population. Methods: A retrospective review of all patients treated with Sunitinib for RCC from 08/05–11/06 was performed. Data regarding hematologic parameters (e.g. CBC, mean corpuscular volume- MCV), concomitant medications, liver function, and time on therapy (cycle length varied from 4–7 weeks) was recorded. Vitamin B12 and folate levels, iron studies, and thyroid function were recorded if available. A standardized, laboratory-specific MCV was used to define macrocytosis. Results: 43 patients formed the study cohort, receiving a median of 4 cycles (24 weeks) of Sunitinib. Overall 19 (44%) patients developed macrocytosis, at a median of 3 cycles (16 weeks). Of the 31 patients who received > 2 cycles of Sunitinib, 48% developed macrocytosis compared to 33% of the 12 patients receiving =2 cycles. Among all patients with macrocytosis, only 8 (42%) had anemia at the time. Of the 24 patients who did not become macrocytic, 19 (79%) had a continual rise in their MCV during therapy. Other causes of macrocytosis including vitamin B12 and folate deficiency, hypothyroidism, and other medications, did not contribute to the macrocytosis identified in this cohort. On preliminary analysis, it did not appear that macrocytosis was associated with response or toxicity. Conclusions: This is the first study to document the common occurrence of Sunitinib-associated macrocytosis in RCC patients. The risk of macrocytosis increased with duration of treatment. Macrocytosis did not appear to be associated with significant clinical sequelae; however this, as well as the mechanism of macrocytosis, requires further study.

No significant financial relationships to disclose.

Application of the International Germ Cell Consensus Classification (IGCCC) to the Nova Scotia population of patients with germ cell tumors (GCT)

14625

Background: The IGCCC is the internationally accepted, clinically based, prognostic classification used to aid in the management of GCT. The goal of this study was to determine if the IGCCC is applicable to a population based cohort. Methods: A retrospective chart review of all patients diagnosed with GCT in NS between 1984–2004 was completed, and IGCCC classification (good, intermediate, poor) was assigned to each patient based on the site of the primary lesion, the presence or absence of non-pulmonary visceral metastases and pre-chemotherapy tumor marker values. Kaplan-Meier estimates of five year progression free survival (PFS) and overall survival (OS) were calculated for each IGCCC group, for both non-seminomatous GCT and seminomatous GCT. Results: The distribution, PFS and OS are shown below. Conclusions: The IGCCC seems applicable to a population-based cohort, with similar distribution of categories, as well as clear prognostic ability. This project was funded by a Norah Stephen Oncology Scholars Summer Studentship Grant from Cancer Care Nova Scotia. [Table: see text]

[Table: see text]

Chemotherapy in metastatic gastric cancer: population-based perceptions and practice patterns of medical oncologists

Although randomised trials in metastatic gastric cancer have shown a survival benefit from chemotherapy, a significant proportion of medical oncologists do not believe that it prolongs survival or improves quality of life, including those who routinely treat metastatic gastric cancer. There was wide variation in what was considered to be ‘standard therapy’ and a statistically significant difference between what medical oncologists consider ‘standard therapy’ and what they use in every day practice.

Use of technology to facilitate language skills in school-age children

Technology offers numerous possibilities for facilitating language and literacy skills in school-age children and adolescents. Narrative skills can be addressed by the use of specialized programs as well as generic word processing software. Writing skills can be targeted due to the variety of possibilities for input as well as options for supporting spelling and syntax. Reading skills might be improved by the use of programs that focus on decoding, as well as hypertext tools that highlight the use of text patterns or signals.

An analysis of falls in the hospital: can we do without bedrails?

OBJECTIVES

To determine the effects of introduction of a bedrail policy, and an educational program, on patient falls and fall-related injuries.

DESIGN

A prospective "Before and After" design.

PARTICIPANTS AND SETTING

All patients admitted during 1 calendar year in an assessment, treatment, and rehabilitation unit for older people.

INTERVENTION

A policy change for the use of bedrails (restricting their use) and an educational program about their effects.

MEASUREMENTS

Patient fall rates -- all falls and around the bed falls -- and patient and staff injuries.

RESULTS

There was a significant reduction in the number of beds with bedrails attached after the policy introduction (mean of 40/135 vs 18.5/135, respectively, P = .02), but the fall rate (either total or around the bed) did not change significantly. Serious injuries were significantly less common after the bedrail policy was introduced (P = .008), with fewer head injuries.

CONCLUSIONS

Reducing the use of bedrails did not alter patient fall rates significantly, but it was associated with a reduction in serious injuries. Unless it can be shown that bedrails are beneficial, their continued use in older patients must be seriously questioned.

Outcome of advanced stage low grade follicular lymphomas in a population-based retrospective cohort

BACKGROUND

To the authors' knowledge previous reports of patient outcome for advanced stage low grade follicular lymphomas (LGFL) have not been population-based. This is the first report describing the outcome of these patients based on a population-based cohort.

METHODS

A retrospective chart review was performed for all patients diagnosed with advanced stage LGFL between 1987-1995 for the adult population of central and northern Alberta, Canada.

RESULTS

One hundred and fifty-seven patients were diagnosed with advanced stage LGFL. Approximately 45% of patients had died at last follow-up. Treatment was initiated at the time of diagnosis in 87 patients (55%), with alkylating agents used in 66% of them. Of the 70 patients not treated at the initial diagnosis, 69% had been treated at a median of 16.3 months. The overall median survival was 5.9 years. On univariate analysis, significant variables (P < 0.20) included age, B symptoms, symptomatic lymphadenopathy, symptomatic splenomegaly, splenomegaly, Eastern Cooperative Oncology Group performance status, baseline lactate dehydrogenase (LDH), diffuse component on histology, and treatment at the time of diagnosis. By multivariate analysis, the only factors that influenced survival significantly and independently were baseline LDH and B symptoms. An elevated baseline LDH had a hazard ratio of 2.80 (95% confidence interval [CI], 1.65, 4.74) and a median survival of 8.0 years versus 3.6 years (P < 0.0001). B symptoms had a hazard ratio of 2.30 (95% CI, 1.23, 4.30) and a median survival of 6.5 years versus 3.1 years (P < 0.0067).

CONCLUSIONS

Although some patients with advanced stage LGFL enjoy a prolonged survival, 80% of deaths in this cohort were attributable to lymphoma. The median overall survival of 5.9 years offers a less positive perspective on the outcome of these patients than in previous nonpopulation-based reports. This emphasizes the need for further population-based studies as well as new therapeutic approaches, especially those directed toward patients with poor prognostic features such as elevated baseline LDH and B symptoms.

Characterization of the heat shock response in the gills of sea lampreys and a brook lamprey at different intervals of their life cycles

The heat shock response (HSR) was characterized in the gills of two lamprey species that differ with respect to their adult life history. In vivo labelling with [35S]methionine revealed an enhanced synthesis of heat shock proteins (HSPs) having approximate molecular weights of 70 kDa (HSP70) and 90 kDa (HSP90) following heat treatment. Induction of the HSR occurred in larval lampreys (ammocoetes) following temperature elevations of 13-16 degrees C for the parasitic species, the sea lamprey (Petromyzon marinus) and 16-20 degrees C for the nonparasitic species, the brook lamprey (Lampetra appendix). The case in L. appendix represents the greatest increase in temperature required to induce the HSR in gill tissue among aquatic poikilotherms studied to data and induction occurs within a temperature range (25-29 degrees C) not normally experienced by these animals. Western blotting detected the presence of 70 and 90 kDa HSPs and HSP70 levels were greater in post-metamorphic L. appendix than in ammocoetes both before and after heat shock. The HSR of lampreys appears to be induced during times of emergency when large, rapid temperature increases are experienced. The high set-point temperature for induction of the response may be a consequence of both the environments they presently inhabit and their experiences during evolution.

Buckling of redundant expansile stent distal to an oesophageal cancer: endoscopic management

This report describes a complication that occurred as a result of deploying an Ultraflex stent too low in relation to a stenosing carcinoma of the gastro-oesophageal junction. Intermittent kinking of the redundant lower end of the stent caused frequent episodes of total dysphagia. A percutaneous endoscopic gastrostomy was deployed to anchor the redundant portion of the stent within the stomach, allowing it to be shortened with endoscopic stitch cutters. This procedure relieved the episodic dysphagia, and was well tolerated.

Obstetric retrospect

A series of 818 consecutive obstetric patients in a general practice between 1946 and 1970 is analysed in detail. The findings are discussed in relation to other studies from general practice and to current obstetric hospital practice.

Modulus of Natural Rubber Crosslinked by Dicumyl Peroxide III. Some Molecular Interpretations, Possible Refinements of Theory, and Conclusions

The qualitative and quantitative agreement of predictions and results demonstrated in the previous sections is a strong confirmation of the essential validity of all the extremely simplified molecular considerations involved, including the general aspects of the statistical theory of rubber elasticity. We know of no previous experimental study extending over as wide ranges of crosslinking and temperature. In fact the crosslinking and temperature have been varied simultaneously on only a few occasions in previous work. An important advantage of the present work over many previous studies is the fact that measurements are made at very small deformations. Thus the results are expressed in terms of the modulus, defined as the limiting value of the ratio of stress to stain at zero deformation. Consequently, the results are independent of the stress-strain relation or equation of state. This means that no consideration needs to be given here, for example to the difference between the stress-strain relation predicted by the statistical theory of rubber elasticity and that given by the Mooney-Rivlin equation or the empirical equation of Martin, Roth, and Stiehler. The present study has shown that the modulus G includes a considerable component arising from internal energy changes as well as that arising from entropy changes. The energy component at room temperature is of the order of half the total when the degree of crosslinking is that normally used with dicumyl peroxide rubbers. It is concluded that the nonzero value of the modulus when extrapolated to zero crosslinking is due to the energy component of the modulus rather than to entanglements. Entanglements acting as pseudo-crosslinks would serve to increase only the entropy component. The gel point, defined as the minimum degree of crosslinking required to form a network, may be located experimentally as the crosslinking at which the slope of the modulus-temperature relation is zero. The value of the modulus G at the gel point is not zero, but is the energy component under this condition; the entropy component of G at the gel point is zero. The amount of dicumyl peroxide required to crosslink rubber to the gel point is the sum of that wasted by reaction with impurities in the rubber and that required to give one crosslink for each rubber molecule. The former quantity was about twice the latter in the work reported here. The entropy component of the modulus as determined from reported values of equilibrium swelling by the Flory-Rehner equation, is found to be significantly larger than that determined from mechanical measurements. However, the quantity computed is smaller than the sum of the entropy and energy components as determined from crosslinking considerations or from mechanical measurements. It increases linearly with crosslinking at a slightly greater rate than the modulus or the entropy component of the modulus. It is concluded that the “front factor” sometimes introduced in statistical theory considerations cannot differ from unity by more than about 7%. The difference is even less than this if allowance is made for entanglements functioning as pseudo-crosslinks.

Physical Constants of Different Rubbers

Where a range is given, there are available several observations which differ. In most cases the differences are thought to be real, arising from differences in the rubber rather than from errors of observation. Where a single value is given, it is either because no other observations are available or because there seems to be no significant disagreement among values within the errors of observation. Where values are not given, data have not been found. Where dashes are shown, either the physical measurement is impossible or the constant in question is not adequately defined under the given conditions. 50 phr means “50 parts of carbon black by weight per 100 parts of rubber”, corresponding to a volume fraction of about 0.2. The values shown refer to specific vulcanizates cited in the corresponding references. Other vulcanizates may yield a broader range of values. The metric technical unit “kilogram force” or “kilopond” has been taken as 9.80665 newtons (980 665 dynes). Where an undefined calorie has been used by the respective authors, it has been taken as the thermochemical calorie equal to 4.1840 joules. Values are given for constants at a temperature of 25°C and a pressure of 1 normal atmosphere = 1.01325×105 Pa (where 1 Pa = 1 N/m2 = 10 dyn/cm2 = 10−6 bar).

Long-Time Creep in a Pure-Gum Rubber Vulcanizate: Influence of Humidity and Atmospheric Oxygen

The long-time creep of natural rubber cured with a conventional sulfur-accelerator recipe containing no filler can be conveniently shown near room temperature by a plot of ΔE/E1 with a double-abscissa scale, one marked in units of log t and the other in units of t. When experimental data from the present work and from previous studies reported in the literature are plotted in this manner it is noted that invariably the first scale yields a linear relation at short times and the second a linear relation at long times. The limiting linear relations just mentioned suggest the two-constant Equation (2), already proposed as a general creep equation for many materials. In the case of rubber the range of values of t investigated is from about 10 ms as studied by previous investigators to about 70 days in our work and other studies. Any significant deviations from the equation can be noted by inspection of the double-abscissa plot. We found that the equation furnished an excellent representation of almost all our experimental data up to the longest times. In one instance in our work and in a few other cases there was a prerupture increase of ΔE/E1 above the values given by the equation. This behavior can reduce somewhat the upper limit of validity of the general equation. The constants A and B can be evaluated from experimental observations of ΔE/E1 by solving two simultaneous equations obtained from the values at the longest time, at one minute, and at an intermediate time. In the present work, the constant A was essentially the same (about 2.4%/ (unit log t)) when the atmosphere surrounding the specimen was a vacuum, dry nitrogen, or dry air. The value was raised when the atmosphere was room air at 35% relative humidity and became about 4%/ (unit long t) when the air was saturated with water. The constant B was raised tenfold when the atmosphere was dry air instead of dry nitrogen. It was further increased by a factor of about 2, when the air was saturated. The value of B for the specimen in an atmosphere of stagnant room air was still greater than this by another factor of more than 2. It is possible that this atmosphere contained autocatalytic degradation products or other constituents which were removed when the air was bubbled through water or passed over CaCl2. The approximate boundaries of three different regions of time are determinable from the ratios A/B. In the first region, where t is less than 0.1(A/B), ΔE/E1 is approximately linear with log t. In the second region, where t is between 0.1(A/B) and 4.343 (A/B), ΔE/E1 is not linear with either log t or t. In the third region, where t is greater than 4.343 (A/B), ΔE/E1 is approximately linear with t. A fourth region of anomalous increase preceding rupture is sometimes found, especially when B is large.

Modulus of Natural Rubber Crosslinked by Dicumyl Peroxide. I. Experimental Observations

Natural rubber mixed with varying amounts of dicumyl peroxide are crosslinked by heating 120 min at 149° C. The quantitative measure of cross- linking was taken as the amount fp of decomposed dicumyl peroxide, the product of p, the number of parts added per hundred of rubber and f the fraction decomposed during the time of cure. The shear creep modulus G was calculated from measurements of the indentation of a flat rubber sheet by a rigid sphere. The glass transition temperature Tg, was raised about 1.2° C for each part of decomposed dicumyl peroxide. Above (Tg+12) the modulustemperature relations were linear with a slope that increased with increasing crosslinking. The creep rate was negligible except near the glass transition and at low values of fp. Values of G, read from these plots at seven temperatures, were plotted as a function of fp. The linearity of the two plots permits the derivation of the general relation: G=S(fp+B)T+H(fp+B)+A where A, B, H, and S are constants. The lines representing G as a function of fp at each temperature all intersected near the point, fp=0.45 phr, G=2.70 Mdyn cm−2(0.270 MN  m−2). . The constants were evaluated as A=2.70 Mdyn cm−2,B=−0.45 phr, S=5.925×10−3 Mdyn cm−2(phr)−1 K−1 and H=0.0684(Mdyn cm−2) (phr)−1. This equation represented satisfactorily all the data obtained at temperatures from —50 to +100° C for values of fp from about 1 to 24 phr.

Creep of Pure-Gum Vulcanizates of Natural Rubber

The creep of vulcanizates of natural rubber cured with varying amounts of dicumyl peroxide was compared with that of vulcanizates cured by typical conventional surfur-accelerator systems. The measurements involved indentation of a flat rubber disk as a function of time t and temperature T. The product of shear compliance J and T as a function of log t was represented by a family of curves with T as the parameter. For the vulcanizates cured with the sulfur-accelerator system, previous work has shown that the individual curves could be shifted along the abscissa to yield a single continuous curve with a slope which increased from a negligible value to a maximum and then decreased, continuing through a region of minimum slope which extended over about 7 decades of time before ending in a region of increasing slope. The value of the creep was 1.5–2.0% per decade in the region of minimum slope. When the same procedures were applied to the vulcanizates cured with dicumyl peroxide, the individual curves of JT against log t at each temperature did not yield a single continuous curve when shifted. In a limited region just above the glass transition temperature, the creep was appreciable, but neither a constant-activation-energy shift nor a Williams-Landel-Ferry shift was satisfactory. Above this region it was clearly impossible to obtain a single curve since the compliance-temperature product at a given time increased with increasing temperature while the corresponding creep of the dicumyl peroxide vulcanizates was generally too small (&lt;0.5% per decade) to be measured between 5 and 600 seconds, except when the compound contained less than 2.5 parts of effective dicumyl peroxide. Outside of these regions the shear modulus was found to increase linearly with temperature. The investigation included temperatures as high as 100° C and effective dicumyl peroxide concentrations as high as 25 parts per hundred of rubber. The present results for the modulus and creep of dicumyl peroxide systems show good agreement with the published data of Chasset and Thirion (obtained by stress relaxation at 30° C) and of Plazek (obtained by a torsion pendulum) over the ranges they investigated.

Creep of Pure-Gum Rubber Vulcanizates from Indentation-Time Measurements

The compliance J (limit of the ratio of strain to stress at zero deformation) has been determined from measurements of the indentation of a flat rubber surface by a rigid sphere, as a function of time t and temperature T. The results are subjected to two successive operations: (1) Jis multiplied by the absolute temperature T and (2) an empirically-determined number is added to the logarithm of the time at each temperature to make the values of JT agree as well as possible. For natural rubber from 25° to −40° C the shift required appears to correspond to a constant “activation energy” of 38kcal/mole; from −40° to − 60° C the shift is in quite good agreement with that predicted by the equation of Williams, Landel, and Ferry. Butyl rubber yields an “activation energy” of 20 kcal/mole while styrene-butadiene rubber gives a value of 22 kcal/mole. The resulting curve of JT against log t shows a sigmoid form with an increase of slope over 2 to 3 decades and a decrease at higher values. There is usually an extended region of nearly constant slope corresponding to the conditions of normal use of rubber products. For natural rubber this slope is 1 to 2% per decade; for the synthetics it is appreciably higher, reaching a value of 15% per decade for nitrile rubber. This behavior differs from that of a classical idealized polymer network, for which the compliance would approach an equilibrium value at long times.

Crystallization and Second-Order Transitions in Silicone Rubbers

In the course of an investigation to determine which rubbers might be suitable for use at low temperatures, interferometric measurements of the length-temperature relationships of silicone rubbers have been made. Crystallization was found between −60° and −67° C in Dow-Corning Silastic X-6160 and in General Electric 9979G silicone rubber, the latter of which contains no filler. Crystallization between −75° and −85° C was found in Silastic 250. Melting occurred over a range of temperature above the temperature of crystallization. The volume change on crystallization varied from 2.0 to 7.8 per cent. No crystallization or melting phenomena were observed in Silastic X-6073 between −180° and +100° C. All types of silicone rubber exhibited a second-order transition at about −123° C, the lowest temperature at which such a transition has been observed in a polymer. The coefficient of linear thermal expansion of silicone rubbers containing no filler was found to be about 40×10−5/degree C between −35° and 0° C.

Refractive Index of Natural Rubber for Different Wave Lengths

The refractive index of natural rubber and its variation with temperature and wave length are those which would be predicted for a similar hydrocarbon of low molecular weight. A two-constant equation of the Cauchy or Sellmeier type is inadequate to express the relation between refractive index and wave length for rubber. For convenient reference the best values resulting from the present investigation are recapitulated in Table VI.

Values of the Physical Constants of Rubber

A critical survey has been made of the values of 16 basic physical constants of rubber in the fields of mechanics, heat, optics and electricity. The value for each constant which seems most reliable has been indicated and, when necessary, has been corrected to the standard conditions of normal atmospheric pressure and a temperature of 25° C. The values have been given for rubber in four different forms: purified hydrocarbon, commercial raw rubber, soft vulcanized rubber containing 2% combined sulfur and hard rubber containing 32% sulfur. The survey indicates that there are significant gaps in present knowledge of the fundamental properties of rubber. In some cases data are lacking, while in many others the best values available are not of the accuracy required for present-day scientific and industrial work. This paper may therefore serve not only as a summary of selected values of the different constants, but also as a basis for the planning of future investigations.