Influence of molecular weight and molecular weight distribution on mechanical properties of polymers

Abstract

This work reviews the literature published over the last ten years on polymer mechanical properties as a function of molecular weight and molecular weight distribution, Thermal properties, stress‐strain properties, impact, fracture, fatigue, creep, stress relaxation and cracking and crazing are examined for a wide variety of homopolymers and a limited number of copolymers. In general, mechanical properties increase as the molecular weight increases. However, above some limiting molecular weight the mechanical property is usually unaffected. Although much work has been done to describe the effects of molecular weight on mechanical properties, little quantitative correlation exists. The available equations to predict such properties as cracking and crazing, Tg, Tm and tensile strength from molecular characteristics are discussed in detail. However, a more quantitative description incorporating a wider range of mechanical properties would be more useful. This would facilitate use of the vast amount of information available and enable it to be applied more readily to new polymer systems.

On the abrasive wear behaviour of mineral filled polypropylene

“…The modulus of a polymer is not strongly affected by molecular weight but is predominantly a function of the crystallinity. Increased crystallinity is associated with increased stiffness, however the work of Margolies(in 27 ) shows that increasing the molecular weight of linear polymers results in a deterioration in the crystallinity, and hence the stiffness of the polymer. The decrease in flexural stiffness reaches a critical point around a molecular weight of 1.75 x 10 6 , above which no further significant decrease in evident The work of Phillips and co-workers( 2 0) showed that in the absence of orientation, an increase in flexural modulus can be attributed to enhanced crystallinity.…”

Empirical models for end-use properties prediction of LDPE: application in the flexible plastic packaging industry

“…In the proposed model (Equation 4), the stiffness decreases as the fluidity index increases; this is in accordance to literature data for samples that doesn't present high degree of orientation. Kundu et al 6 found an inverse correlation between modulus and MW for polyethylene. Stiffness = a * FI + b * density + c (4) Latado et al 3 tested many grades of polypropylene and propylene/ ethylene copolymers to develop empirical models in order to predict the stiffness.…”

“…Kundu et al 6 showed the influence of various film preparation procedures on the crystallinity, morphology and mechanical properties of pure linear low density polyethylene. According to them, quenching of films reduces the degree of cristallinity whereas natural cooling allows crystals to grow to a stacked lamellar structure or to a higher spherulite embedded in lamellar structure and hence increases in cristallinity.…”

“…Thus, these properties are much influenced by film production process. Film obtaining process determines properties associated to the molecules orientation, degree of crystallinity, film thickness and imperfections 6 . In the case of the films ultimate tensile strength, the molecular weight increase tends to increase the polymeric chains orientation during the process; thus, the linking forces between them increase which improvement the MD and TD tensile strength.…”

Cross-Conjugated n-Dopable Aromatic Polyketone

“…[22][23][24][25] The optical band gap (E opt g ) of conjugated polymers typically saturate already at low P n , 26,27 the excellent physical properties associated with commodity plastics (such as mechanical compliance and durability), however, are significantly affected by molecular weight. 28,29 Unfortunately, despite numerous optimizations of the polycondensation reaction to synthesize CPIs based on PFK, molecular weights remained relatively low (P n ∼ 9). 9 To address this shortcoming, we set out to optimize the polymerization conditions in order to synthesize higher molecular weight cross-conjugated aromatic polyketones with potentially interesting optoelectronic properties.…”