Viscoelastic Properties of Poly(pivalolactone)

Abstract

The maximum shear rates used in ref 9 ranged from 1.8 X lo4 s-' at 345 MPa (50000 psi) to 3.8 X lo5 s-' at atmospheric aressure.(18) 2.ABSTRACT: The viscoelastic properties of poly(pivalo1actone) (PPL) have been investigated in the linear range using stress-relaxation and dynamic-mechanical measurements. Under the conditions that the sample was isotropic and insensitive to relative humidity, Ferry's reduction method was applied without using translations along the vertical axis. A horizontal shift factor was determined at each temperature, which satisfactorily agreed with the WLF equation in the transition region. The apparent activation energy of PPL was temperature dependent and passed through a maximum near Tg whose value was found to be 369 f 3 K. The relaxation spectrum was calculated according to the first method of approximation of Schwarzl and Staverman, and it was found to be flat with a complicated fine structure. Two absorption peaks were determined. The low-temperature y peak, around 300 K, was ascribed to a relaxation process in the crystalline phase of the polymer while the high-temperature p peak was related to the glass-transition process.Among polylactones based on the skeletal formula (-CH2CR1R2C00-),, poly(pivalo1actone) ( P P L ) has been the most extensively studied because of its technological i m p~r t a n c e . ' -~ The practical and technological interests appeared since the polymer has been commercially spun to give fibers.Q Moreover PPL has been f o u n d to have reinforcing properties when prepared in copolymers of the general s t r u c t u r e ABA where A represents a PPL block and B an elastomer, for example, poly(cu-methyl-a-npropyl-P-propiolactone) ( P M P P L ) . The mechanical properties of PPL/PMPPL ABA copolymers were reported similar to those of commercial styrene-butadiene-styrene (SBS) and styrene-isoprene-styrene (SIS) copolymer^.^ More recently, it was shown that grafting of short ( M , -500-4000) chains of PPL onto various elastomeric backbone polymers, including ethylene-propylene-diene, a l t e r n a t i n g ethylene-ethyl a c r y l a t e copolymer, and poly(ethy1 acrylate), produced a new type of thermoplastic elastomer with outstanding physical properties, such as solvent resistance resilience, abrasion resistance, and h e a t and aging ~t a b i l i t y . "~ ABA triblock copolymers containing 35-45% PPL made f r o m polyisoprenes ( M , -40000) could be melt-spun into fibers showing excellent mechanical properties.1° In each case, t h e o u t s t a n d i n g properties of these P P L -g r a f t elastomers were related t o the hard segments of PPL which act as cross-linking sites and reinforcing filler particles. In view of the commercial importance of PPL, its thermal and crystalline properties have been investigated.11-19 But surprisingly, its mechanical properties have not been studied despite the importance of t h i s investigation i n order t o know the performance of PPL as a commercial film o r fiber.It is then the purpose of the present paper t o investigate the...

Crystallinity-Induced Biodegradation of Novel [(R,S)-β-Butyrolactone]-b-pivalolactone Copolymers

“…No glass transition attributable to the PPVL block was detected, due to the rather low PPVL content of the copolymers and to the well-known difficulty to inhibit crystallization of this polyester by quenching. As a matter of fact, the few conflicting data on the glass transition of PPVL available in the literature were obtained from relaxation techniques rather than by DSC (6 and 96 °C from dynamic-mechanical measurements, 137 °C from dielectric measurements).…”

Synthesis and Characterization of Poly(isobutylene-b-pivalolactone) Diblock and Poly(pivalolactone-b-isobutylene-b-pivalolactone) Triblock Copolymers

“…This clearly indicated microphase separation in the block copolymers. Although several data on the T g of PPVL were reported using relaxation techniques, 26,27 the T g of PPVL segment was not detected using DSC. To calculate the degree of crystallinity, ∆H m 0 ) 148.4 J/g was taken for 100% crystalline PPVL from the literature.…”

Solid-state relaxation properties of poly(α-methyl-α-n-propyl-β-propiolactone)/poly(vinyl chloride) miscible blends

“…The plateau is due to the crystalline part of the polymer and it was suggested before that it corresponds to the thermal expansion of its crystalline portion followed by the loosening of the entanglements of its amorphous portion. 27 The behavior of the 75/25 PMPPL/PVC blend is very similar to that of PMPPL, except that the plateau is not as well defined due to its lower degree of crystallinity (Table I).…”

“…For PMPPL, previous measurements indicated a linear viscoelastic limit at 2.5% by the two methods cited above. 27 For PVC, measurements conducted at 305 and 283 K indicated a linear viscoelastic limit at 1.3% by the relaxation method at short times and the hysteresis loop method and at 1.0% by the relaxation method at long times.28 These values agree with those reported by Jamshid.29 In view of the results cited above and since the linear viscoelastic limit is found at higher strain values at temperatures higher than Tg,25,26 all stress relaxation data reported in this study obtained at a strain level of 0.6%, well within the linear viscoelastic limit.…”