Novel Dynamic Viscoelastic Measurements of Polyurethane Copolymer Melts and Their Implication to Tack Results

Abstract

Summary: A series of polyurethane multiblock copolymers with different proportions of hard segments (urethane) to soft segments (polyadipate of hexane‐1,6‐diol), are investigated. Dynamic viscoelastic functions of homogeneous melts in the terminal zone are determined. For the first time, entanglement modulus values of such copolymers are reported, which allows estimation of the packing length. These parameters do not vary with changing the hard‐to‐soft segment ratio, a result that is explained by a compensating effect of the chain architecture. For samples of similar molecular weight, the relaxation time of the terminal zone increases as the hard‐to‐soft segment ratio augments. The adhesives obtained from PUR solutions show a correlation between the elastic modulus and the debonding stress‐strain curves in tack experiments.The storage modulus of the adhesives as a function of frequency at 70 °C.magnified imageThe storage modulus of the adhesives as a function of frequency at 70 °C.

Mechanical Properties of Adhesive Films Obtained from PU−Acrylic Hybrid Particles

“…In essence the PU would appear to act like any low molecular weight crosslinker. Yet this is misleading because, in addition, PU chains are also more densely entangled than the acrylic chains because of the PPG constituting their soft segment (M e ~ 3 -5 kg.mol -1 for the PU 47 while M e ~ 20 -30 kg.mol -1 for the acrylics 48 ). Thus, the PU adds both chemical and physical crosslinks and this is the reason for the significant increase in the small-strain modulus.…”

Fracture of model polyurethane elastomeric networks

“…Details of the data treatments are given elsewhere 5. As expected from the average molecular weight between entanglements ( M e ∼ 3000 g mol −1 for PPG3), the contribution of E e is almost negligible for PU4000, while it is higher for the PU8000/1000 and becomes of the order of 20% for the PU8000. Moduli obtained by the Rubinstein‐Panyukov fits are very close to those obtained by DMA.…”

“…Three different model networks were prepared, varying the PPGs nominal molar mass. The first one, based on a M n,PPG = 4000 g mol −1 , was essentially unentangled, knowing that the PPG average molecular weight between entanglements is around ∼3000 g mol −1 3. The second one was prepared with M n,PPG = 8000 g mol −1 to obtain crosslinks and entanglements.…”

Rheology of Polymer Processing in Spain (1995–2020)

“…The analysis of the SAOS results indicate that the alteration of the values of the elastic and viscous moduli at low frequencies (with G’ > G”) does not affect tack results, as the aforementioned Dahlquist criterion is fulfilled. The liaison between SAOS results and tack results is confirmed in two more papers of this group, on polyurethane solutions [ 105 ] and styrene-butadiene-styrene (SBS) block copolymers [ 18 ], respectively. In both papers it is stated that tack only occurs in formulations which have an elastic shear modulus below 3.3 × 10 5 Pa (Dahlquist criterion).…”